The present invention involves the use of pupil plane filters to enhance optical imaging for both lithography and microscopy. The present invention includes numerous pupil plane filter strategies for enhancing optical lithography. A square pupil plane filter suitably restricts the imaging to a nearly diffraction limited regime. Moreover, pupil plane filters are suitably used in off-axis illumination (OAI) and imaging interferometric lithography (ILL). The techniques of OAI and ILL along with the use of pupil-plane filters are applicable in, for example, any diffraction-limited situation where the limit is imposed by the characteristics of the optical system rather than the transmission medium and where the illumination system is under the control of the experimenter.